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    <!-- 根据输入的三个数字，判断是这一年的第几天
例如：

var year = 2016
var month = 2
var day = 11

// 逻辑代码

// 输出是第 42 天 -->
    <script>
        var year=parseInt(prompt("请输入年份"));
        var month1=parseInt(prompt("请输入月份"));
        var day=parseInt(prompt("请输入日期"));
        var leapYear=(year%4==0 && year%100>0)||year%400==0;
        var commonYear=!leapYear;
        var month=1;
        var total=0;
        while(month<month1){
        if(leapYear && month==2){
            console.log("本月天数为"+29+"天")
            a=29;
        }else if(commonYear && month==2){
            console.log("本月天数为"+28+"天")
            a=28;
        }else if(month==1||month==3||month==5||month==7||month==8||month==10||month==12){
            console.log("本月天数为"+31+"天")
            a=31;
        }else if(month==4||month==6||month==9||month==11){
            console.log("本月天数为"+30+"天")
            a=30;
        }
        total+=a
        month++
        }
        console.log(total+day)
    </script>
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